[Greenbuilding] Cellulose blowing tools/techniques

Fri Jun 1 22:04:08 CDT 2007

Mike et al,
Blowing cellulose behind a scrim does have all of the drawbacks you 
list.  If the scrim is not tight enough, it will bulge out and cause the 
drywallers fits.  Gluing and screwing the drywall seems to help restrain 
the pack, but hitting the balance between a good, dense pack and 
problematic overfill seems to me too much trouble unless you are doing 
it regularly and can develop a feel for the process.  The equipment 
required for damp spray or glue spray is generally not available for DIY.

My choice would be to close the wall and dense pack it.  It can be done 
through the standard holes - provided that they are about two feet 
apart.  Most machines will only reliably pack to dense pack standards 
(3.7 to 4#/ cubic foot) for an eighteen inch radius from the nozzle.

A more reliable technique is to "tube" the cavities.  Drill a single 3" 
hole at the top or bottom of the wall (bottom access avoids the ladder 
or scaffold work and has worked just as well); I make mine about a foot  
to a foot and a half off the floor, for convenience. A smaller pressure 
relief hole at the top helps too. 
Use ten feet (for an eight foot wall height) of semi-flexible tubing, 
1.5 to 1.75" ID, as a nozzle.   (You will need an adapter to mate to the 
standard blowing hose.  Adding a 25 to 50' section of 2" blowing hose as 
an intermediary helps straighten the flow and limit clogs.)
Feed the tube through the hole to the end of the cavity.  Pull it back 
about a foot ( it helps to make the tube in 1' increments to gauge the 
process) and blow to 'refusal' (when the motor starts to whine and the 
hose threatens to clog), then pull the hose out a foot and repeat the 
process.  Repeat until you are at the last six inches of hose.  Hold  
the nozzle right at the opening for the final pack.  If you hold a piece 
of jute sacking around the hose at the opening, it will limit the fluff 
blow-out and allow the back pressure to bleed off.

The cellulose will start by filling the whole cavity loosely, then it 
will begin to pack around the nozzle (end of your hose) and push 
pressure waves out to pack until the resistence overcomes the air 
pressure.  With practice you can pack a cavity with very little mess.  
Dense pack cellulose will not settle; it will block low pressure air 
movement significantly; and it will fill around obstacles, such as 
wiring, bracing or ductwork.  Obviously, if there are fire stops or 
other blockages, a secondary blowing hole beyond the blockage will be 
needed.

Please forgive the monograph, but it seemed that folks had most of the 
techniques but I haven't seen any clear discussion of tubing.  Hope this 
helps.

Bob Klahn

Mike O'Brien wrote:
> Hi, Jefro--
>
> Blowing in dry cellulose through a mesh *can* work. Fibers will blow  
> back out through the mesh and make clouds of cellulose haze, but when  
> it settles you can sweep it up for reuse. The stapled mesh will swell  
> outward if a cavity is overblown, making it hard for the drywallers  
> to compress flat with boards, so watch the amount.
>
> Mike O'Brien
>
>
>
> On Jun 1, 2007, at 3:23 PM, Jefro wrote:
>
>   
>> I have been following this thread with grave interest, as I am in the
>> same position---about 3 or 4 weeks away from installing cellulose into
>> my 2x10 wall cavities.
>>
>> As I see it, I have three options if I want to do the job myself---and
>> given the financial realities of house building, I will be doing it
>> myself.  I'll be using Cocoon cellulose, which is manufactured  
>> about 150
>> miles from home, and installing with a rented blower.  This will be a
>> dry install.  Options are:
>>
>> - sheetrock first, drill holes and install as a retrofit per manuf.
>> instructions
>> - install poly netting and blow through it, and hope for the best
>> - sheetrock the lower half of the wall, fill with cellulose, then  
>> do the
>> same with the upper half
>>
>> I can see advantages and disadvantages to each method.  Will  
>> probably do
>> a test run using each method on a couple of different wall sections
>> first, to see which goes fastest and which seems to fit most  
>> densely and
>> thoroughly.  I'll also do a "settle test" by drilling holes at the
>> ceiling in a couple of months and topping off where necessary.
>>
>> For the third method, I wonder if it would be advantageous to  
>> forego the
>> blower, just sheetrock up 4 feet and dump the stuff into the well, and
>> then compress or tamp down by hand before adding the top layer.  Any
>> thoughts?
>>
>> BTW, I estimated about 105 "bags" of insulation per the manufacturer's
>> recommended coverage.  (They list for horizontal blowing, mine is  
>> inside
>> vertical walls so I added 10%.)  The hardware store rents the  
>> blower for
>> free if you buy enough insulation.  That means that ALL of the wall
>> insulation to fill 2x10 walls in a 1600sf two-story house for approx.
>> R29 walls, will cost about $1100.  That beats fiberglass by a long,  
>> long
>> margin, though of course doesn't count the roof.
>>
>>
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